1. Field of the Invention
This invention relates to a pattern recognition system or more in particular to a pattern recognition system in which patterns of unknown and standard characters are described in the form of Freeman direction codes so that a minimum value of the sum of the differences between the two types of codes is used as a measure for determining the similarity between the two types of patterns thereby to recognize the unknown pattern.
2. Description of the Prior Art
The recognition of characters of a font of fixed shape such as machine-printed characters is comparatively easily effected by a matching process such as a correlation between an input pattern of character and a standard pattern of character. In the event that a plurality of fonts of machine-printed characters are involved, however, there are as many different shapes as fonts for a character to be recognized. Further, the shape of a hand-printed character is quite different depending on who wrote it or on the frame of mind at the time of writing it. In a conventional system for recognition of hand-printed characters, such variations of the shape of characters are absorbed by extracting very rough features of certain points of the character. This system, even though capable of recognizing hand-printed numerals, encounters a very great difficulty in recognizing hand-printed alphanumerics or hand-printed Japanese katakanas which involve a considerable number of characters.
Another system for recognition of hand-printed characters is such that line components of a hand-printed character are approximated by small straight lines and the result of such approximation is described in the form of Freeman direction codes thereby to recognize the character. In this particular system, the variations in the shape of hand-printed characters are absorbed by the sequential logic with direction codes as an input. This system has the disadvantage of a great amount of internal state of the sequential logic required for absorbing the variations in character shape in a satisfactory manner. Also, since the last-mentioned system relates to a deterministic decision as to "yes" or "no", it is difficult to accomplish recognition in the presence of a character variation which had not been taken into consideration in forming the sequential logic.